It is often necessary to determine the physical properties and characteristics of materials prior to employing them for any specified purpose. The invention pertains to the field of hardness testing of metallic sheet materials. This is simply a measurement of the strength of a sheet material under compressive loading. Hardness is a characteristic property of interest when one wishes to employ a specific material for, for example, defensive purposes, i.e. in the art of defensive armor. This property may be measured by determining the resistance of a material to projectile penetration.
Several methods/scales of reference for hardness of materials have been developed over the years. The Rockwell and Brinell hardness scales are the most common scales presently applied.
The Department of the Army has been employing Brinell Hardness Testing as a means for determining the resistance of armor materials to projectile penetration. This hardness testing measurement is defined as the resistance which a material specimen elicits to permanent indentation caused by a penetrating device by which predetermined loads are applied. It is used to measure the strength and/or hardness of a material under compressive loading.
The current method (Brinell Hardness Testing) for testing materials requires the use of a clamping device for supporting the test specimen while a predetermined load is mechanically applied to a 10-mm ball. The applied force may be as great as 3,000 kg depending upon the thickness and strength of the specimen material being tested. The indentation caused by the applied force is then evaluated using a Brinell microscope to measure the diameter of the impression. This measurement is then converted to Brinell hardness using the ASTM E10-66 conversion chart--published by the American National Standards Institute in accordance with the American Society for Testing and Materials (ASTM).
It is important to note that in the conventional method described above, the specimen to be tested must be physically brought to the testing apparatus and clamped thereto prior to applying the thousands of kilogram force necessary to place an indentation on the specimen. Therefore, because the material to be evaluated must be physically brought to the testing apparatus, oftentimes a specimen of the material is cut to represent the entire material for evaluation. This can destroy the structure and purpose for which the material was employed--i.e., armor on a vehicle. Moreover, due to the clamping mechanism employed, the conventional hardness testing apparatus is only able to test the area of the specimen which is not under the clamping mechanism. Stated differently, one is unable to test the hardness of the area of the specimen which is used for the purposes of clamping the tester thereto. Consequently, the conventional tester can only test an area within, for instance, four inches of the edge of a specimen plate due to the physical constraints described.
The inefficiencies of this prior art method are two-fold. (1) The material to be tested must be either physically removed from the machine/vehicle/structure to which it is affixed or portions of it cut or removed in order for the measurement to be made. Aside from potentially destroying the purpose for which the material was employed, the dismantling may be inconvenient as well as time consuming and it may require the employ of additional manpower. (2) And, since a portion of the specimen is required to facilitate the clamping of the tester thereon, one is limited in the portion of the specimen which may be tested.
Attempts have been made to overcome some of these inefficiencies. U.S. Pat. No. 4,199,976, issued to John C. Edward, teaches a mobile hardness testing apparatus which employs an electromagnet for magnetically attaching the testing apparatus to cylindrical materials to be tested. A clamping assembly is, therefore, not required. The teaching of this patent is directed to the testing of pipes and pipe collars. This testing apparatus is provided with a shaft member having an unidentified penetrator attached thereto. The penetrator is hand operated.
Although this prior art reference does make an attempt to overcome the inefficiencies described above, nowhere does the reference teach the application of the testing apparatus to evaluate metallic sheet materials--or armor materials. It merely teaches the use of one electromagnet for magnetically attaching the testing apparatus to a pipe or pipe collar to be evaluated. The hardness of a pipe or pipe collar is very much less than the hardness of metallic sheet material for which the present invention is intended to evaluate. One would not consider the teaching of U.S. Pat. No. 4,199,976 to employ an electromagnet having the strength required herein. Moreover, based on this teaching, no motivation would be present for employing two electromagnets, as required by the Magnell Hardness Tester. The patent is silent to some of the critical elements employed herein to assist in overcoming the deficiencies described as well as to simplify the measurement process.
The present invention has been designed to overcome all of the inefficiencies described above, as well as permitting the hardness measurement of sheet materials to be performed using the invention. When employing the present invention, the material to be tested need not be physically removed from the structure to which it is affixed. The present invention may be used directly on, for example, flat vehicular surfaces. The Magnell Hardness Tester is portable. It does not require the presence or use of a permanent or stationary work table.
Moreover, the present invention, does not require the use of a clamping means. Therefore, the test area of a specimen is in no way restricted. And, the thickness of the test specimen, which in the prior art methods would need to be considered for clamping purposes, is not an issue herein. There is no upper limit as to the thickness of a test material which may be evaluated by the present invention.
The present invention overcomes the current deficiencies in the prior art, and serves to satisfy a long overdue need for an efficient hardness tester apparatus.